Oxygen sweetening process



g- 19, 1953 G. H. IMEGUERIAN ETAL 2,848,374

OXYGEN SWEETENING PROCESS Filed June 6. 1955 is Ema km m k m Q\ m N .WM. v m wv N I QQN INVENTORS:

Garb/s H. Meguerion y William P. Fairclrlld m 9% AT T 0RIVE' Y naphthas.

'tillate.

United States Patent OXYGEN SWEETENING PROCESS Garbis H. Meguerian, ParkForest, 11]., and William P. Fairchild, Munster, Ind., assignors toStandard Oil Company, Chicago, 111., a corporation of IndianaApplication June 6, 1955, Serial No. 513,362

9 Claims. (Cl. 19629) This invention relates to the sweetening of sourpetroleum naphthas.

An object of the invention is the catalytic oxidation of mercaptanspresent in petroleum naphthas to produce a naphtha essentially free ofmercaptans. Another object of the invention is a sweetening processwhich is particularly applicable to sour virgin naphthas. Yet anotherobject is a sweetening process wherein refractory sour naphthas arerapidly sweetened. A further object is a process wherein sour naphthasare sweetened without considerable color degradation. Other objects Willbecome apparent in the course of the detailed description of theinvention.

'In this process, sour petroleum naphthas are sweetened by contact withan aqueous solution in the presence of free-oxygen. The aqueous solutionconsists ofan alkyl phenol mercaptan solubility promoter, an alkylenepolyamine mercaptan solubility promoter, alkali-metal hydroxide, a.copper-polyamine complex mercaptan oxidation catalyst and the remainderessentially water. The process is carried out at a temperature ofbetween about 40 F. and 200 F. for a time sufficient to convertessentially all the mercaptans in the sour naphtha to disulfides. Thesweet naphtha is separated from the aqueous solution.

The sour petroleum naphthas which are charged to the process of theinvention may be any mercaptan-containing naphtha which is derived frompetroleum or from a hydrocarbon conversion process. The process isapplicable to all sour hydrocarbon fractions boiling in the naphtharange, i. e., between about 100 F. and 430" F.

at atmospheric pressure. Examples of sour petroleum naphthas are virginlight naphtha, virgin heavy naphtha, absorption naphtha, thermallycracked naphtha, catalytically cracked naphtha, and mixtures of thesenaphthas. Virgin naphthas are much less amenable to oxidation sweeteningthan are either the thermally cracked or catalytically cracked naphthas.The process'of this invention is particularly effective with theserefractory virgin The process may also be utilized on materials boilingin the kerosene and distillate fuel range when theseheavier-than-gasoline distillates are of moderate sulfur content andparticularly are low in alkyl phenol content.

The process is carried out by contacting the sour naphtha with anaqueous solution in an amount at least suflicient to form a distinctaqueous phase. More than this amount of aqueous solution is usuallyutilized. In

general, between about volume percent and about 100 volume percent ofaqueous solution is used, based on sour naphtha charge.

The contacting is carried out in the presence of freeoxygen which may beintroduced either as air, cylinder oxygen, or in the form of anoxygen-furnishing cornpound, such as hydrogen peroxide. At least enoughfreeoxygen is present to produce an essentially sweet dis- Since somesweetening normally takes place in the storage tanks subsequent to thesweetening operation,

'2 it is not always'necessary to complete the sweetening in themercaptan oxidation zone.

The process is carried out at a temperature between about 40 F. andabout 200 F. It is preferred to operate at the lowest temperature thatcontacting time permits. In general, the lower the temperature ofoperation, the longer the contacting time needed to obtain completeoxidation of the mercaptan or sweetening of the sour distillate. It ispreferred to operate at a temperature between about .60 F. and F.

The aqueous solution utilized in the process of this invention consistsessentially of water, an alkyl phenol mercaptan solubility promoter, awater-solube alkylene polyamine mercaptan solubility promoter, freealkali-metal hydroxide, a copper-polyamine complex mercaptan oxidationcatalyst and water. At least about 5 weight percent of free alkali-metalhydroxide, such as sodium hydroxide or potassium hydroxide is present inthe aqueous solution. More than this amount may be present up to thesaturation amount. It is preferred to operate with a free alkali-metalhydroxide concentration of between about 10 and 15 weight percent. Inaddition to the free alkalimetal hydroxide, the solution will containalkali-metal small amounts of alkyl phenols appreciably increase thesolubility of mercaptans in the aqueous solution. Thus as little as onevolume percent or less of alkyl phenol may be present in the solution oras much as the saturation amount may be present. It is preferred tooperate with an alkyl phenol concentration between about IOand 20 volumepercent in the aqueous solution. The alkyl phenols may be purecompounds, such as cresol, xylenol,

.ethyl phenol, nonyl phenol, etc., or they may be mixtures of alkylphenols. Particularly suitable mixtures are those derived from phenoliccompound-containing petroleum hydrocarbons such as crackednaphthas,cycle stocks, and some distillate fuels, such as West Texas heater oil.The alkyl phenols derived by caustic treating from naphthas are commonlyspoken of as petroleum cresols. Those obtained by caustic treating ofcycle stocks or heater oils and which boil at about the boiling point ofxylenol, about 400 F. and higher, are commonly known as petroleumxylenols. Other sources of alkyl phenols are wood tars. It is preferredto utilize petroleum cresols or xylenols.

The aqueous solution also contains another mercaptan solubilitypromoter,alkylene polyamine, where each alkylene group contains from 2 to 4carbon atoms. Even very small amounts of-promoter polyamine in theaqueous solution increases the solubility of mercaptans in the solution.For example, as little'as one volume percent-or less. Amounts ofpromoter polyamine up to the saturation concentration of the solutionmay be utilized. The presence of large amounts of promoter polyamine inthe aqueous solution may result in uneconomic losses of the promoterpolyamine to the sweet oil. It has been found that by operating with notmore than about 8 volume percent of promoter polyamine in the aqueoussolution that the loss of material to the sweet oil may be reduced toavery low and economic amount. It is. preferred to operate with anaqueous solution containing promoter polyamine in an amount betweenabout 3 and 8*volume percent.

- polyamine.

j propylene tetramine,

These alkylene polyamines may be utilized in C. P. grade,

However, any polyamine which is sufiiciently soluble to produce aconcentration of at least the preferred amount is suitable for use inthe process. Examples of polyamine which may be used as mercaptansolubility promoters are ethylene diamine, diethylene triamine,triethylene tetramine, tetraethylene pentamine, propylene diamine,dipropylene triamine, tripropylene tetramine, tetrapropylene pentamine,butylene diamine, and dibutylene triamine. These promoter polyamines maybe utilized alone or in admixture with each other in either the C. P.grade, technical grade, or in commercial grades. The commercial grade ofdiethylene triamine is a preferred source of promoter alkylenepolyamine.

There is present in the aqueous solution a mercaptan oxidation catalystwhich is the complex formed by the reaction of a water-soluble coppersalt and a hereinafter defined alkylene polyamine. The complex isprobably a chelate. 4

The copper salts utilized may be organic or inorganic salts which areappreciably soluble in water. Examples of water-soluble copper saltswhich are suitable for use in the. formation of the catalyst of theinvention are cupric acetate, cupric bromate, cupric bromide, cupricchlorate, cupric chloride, cupric fluoride, cupric fluosilicate, cupricformate, cupric lactate, cupric nitrate, cupric sulfate, cupricmethanesulfonate, cupric ethanesulfonate, benzenesulfonate, and cuprictoluenesulfonate. These salts may be used either in the anhydrous formor in the hydrated form. The widely available and relatively inexpensivecupric sulfate, sold as blue vitriol, i. e.,

CuSO .5H O

is a preferred water-soluble copper salt.-

The other component of the catalyst is an alkylene The alkylene groupmay be either ethylene or propylene. The catalyst alkylene polyaminesmay contain one or more alkylene groups. It is preferred to utilizethose alkylene polyamines which are very water soluble andsimultaneously of relatively low oil solubility. Examples of thealkylene polyamines which may be utilized in preparing the catalyst areethylene diamine, diethylene triamine, triethylene tetramine,tetraethylene pentamine, propylene diamine, dipropylene triamine, triandtetrapropylene pentamine.

the technical grade, or the commercial purifies. The commerciallyavailable grade of diethylene triamine is a preferred source of alkylenepolyamine for use in the preparation of the oxidation catalyst.

The catalyst is prepared by reacting, in an aqueous medium, thewater-soluble copper salt and the alkylene polyamine. Sufiicientalkylene polyamine is added to the aqueous medium to complex all of thecopper salt. The particular amount of alkylene polyamine added isdependent upon the particular alkylene polyamine being used. It appearsthat when utilizing ethylene diamine or propylene diamine that thecomplex is tetrahedral and contains two moles of the diamine and onegram atom of copper ion. More simply, the complex can be prepared byslowly adding the polyamine to a concentrated solution of copper salt inwater until a blue precipitate appears. The presence of excess amine inthe aqueous medium containing the complex salts out the complex in theform of a blue solid. The aqueous medium containing dissolved complex isa blue color. A complex essentially free of excess polyamine is obtainedby decanting the aqueous medium from the precipitated blue solid anddrying the solid at moderate temperature. Or a solution of complex inwater of known concentration can be prepared by adding polyamine to anaqueous solution of copper salt until the first appearance ofprecipitate; the precipitate can be redissolved by the addition of water4 to the preparation vessel. In any event, the presence of excesspolyamine has no deleterious effect on the catalytic activity of thecopper-polyamine complex.

The aqueous solution contains at least a catalytically effective amountof the copper-polyamine complex catalyst. In general, the aqueoussolution will contain between about 0.02 and 1 weight percent,calculated as copper, of the catalyst. More usually the catalyst contentwill be between about 0.1 and 0.3 weight percent as copper. The largeramounts of catalyst have a favorable effect on the rate of mercaptanoxidation.

The results obtainable with the process of the invention are illustratedby the following Working examples. These examples are not to beconsidered as limiting the scope of the invention.

Two types of catalyst polyamine complexes were prepared and utilized.One complex was prepared by dissolving one gram of cupric sulfatepentahydrate in 5 ml. of Water and 2 ml. of technical grade ethylenediamine was added to the salt solution. The addition of more ethylenediamine to the solution resulted in the precipitation of a blue solid.The other solution was prepared by adding one gram of cupric sulfatepenetahydrate to 8 ml. of Water and 7 ml. of diethylene triamine. Theaddition of more polyamine caused the precipitation of a blue solid. Inall cases, the copper polyamine complex containing aqueous media weredeep blue in color. To prepare the catalyst containing aqueous alkalinemedia, portions of the preformed complex solutions were added to theaqueous alkaline media.

Tests were carried out on sweetening of our distillates using a virginnaphtha boiling over the range of about 100 F. to 325 F. and a thermallycracked heavy naphtha boiling over the range of about 200 F. to 400 F.

TEST 1 In this test, the efiectiveness in sweetening of promoterpolyamines was compared with monoethanol amine and butyl amine. The sournaphtha was a virgin naphtha having a mercaptan number of 28 (mg. ofmercaptan sulfur per 100 ml. of naphtha). The aqueous solution consistedof 20 volume percent of the particular amine and the remainder was acresylate solution providing 10 volume percent of petroleum cresols and8% of free sodium hydroxide. The sour naphtha and the aqueous solutionwere contacted at F. utilizing 20% of aqueous solution based on sournaphtha charged. With each amine, after sweetening a portion of the sournaphtha, the sweet naphtha was decanted from the aqueous solution phaseand the separated aqueous solution Was used to contact another portionof the sour naphtha. The catalyst was a copper-diethylene triaminecomplex and was present in an amount equivalent to 0.15 weight percentof copper. In Run No. l, the sour naphtha was contacted with solutioncontaining no amine in order to determine the effectiveness of thepetroleum cresols as sweetening catalysts. The results of thls test areset out in Table I.

Table I Sweeten- Run Amine Treats ing Time,

Minutes 1 None l 60 Butyl amine l 45 Monoethanol amine l 20 The datashow that the monobutyl amine is only slightly more etfective as, acatalyst than the petroleum cresols. Monoethanolarnine is a bettercatalyst than monobutyl amine but is very much poorer than thealkylenepolyamines, ethylene diamine, and diethylene triamine. In thistest, commercial grade diethylene triamine was used.

TEST 2 In this test, the virgin naphtha was sweetened utilizing anaqueous solution containing 4 volume percent of diethylene triamine, 20%of petroleum cresols, of free sodium hydroxide, and the remainderessentially water. The sour virgin naphtha had a color of +30 Saybolt.After sweetening, using a catalyst complex consisting of copper anddiethylene triamine in an amount of 0.15 weight percent of copper, thecolor of the sweet naphtha was +25 Saybolt.

TEST 3 In this test, thermally cracked heavy naphtha having an initialcolor of 14 Saybolt was sweetened utilizing the aqueous solution of thecomposition shown in Test 2. The sweetening was carried out at 100 F.The color of the sweet thermally crack-ed naphtha was 4 Saybolt.

The loss of color is believed due to the presence of dihydroxybenzenecompounds in the thermal naphtha which are converted to color bodiesduring the sweetening process.

TEST 4 In this test, the effect of a sweetening process on the octanenumber and lead susceptibility of the sweet naphtha was determined. Thefeed was a virgin naphtha having a mercaptan number of 9. The aqueoussolution consisted of 10 volume percent of diethylene triamine, 18volume percent of petroleum cresols, 9 weight percent of sodiumhydroxide, water and a copper-diethylene triamine complex sufiicient togive 0.3 weight percent of copper. The sweetening was carried out at 85F. and 4 volumes of sour naphtha were used per volume of aqueoussolution. Special precautions were taken to avoid the loss of lowerboiling hydrocarbons during the sweetening procedure. The sour naphthahad a CFR-R octane number of 55.8 and with 3 cc. of TEL had an octanenumber of 75.9. The sweet naphtha had a CPR-R clear octane numberof.55.9 and with 3 cc. of TEL'had anoctane number of 76.0.

This test shows that, if anything, sweetening by the process of thisinvention has a slight beneficialeffect on the leaded octane numberof'the sweet naphtha.

TEST 5 In this test, the eflfect of having both cresols and promoterpolyamine present in the aqueous solution was studied. The sour naphthawas a virgin naphtha having a mercaptan number of 32. The sweetening wascarried out at a temperature of 75 F. The catalyst consisted of acopper-ethylene diamine complex and was present in an amount sufiicientto introduce 0.2 weight percent of These data show that in the absenceof the polyamine, sweetening does take place at an appreciable rate, butthe color of the sweet oil is markedly reduced from the +30 Sayboltcolor of the sour naphtha. The promoter polyamine alone producedsweetening in a shorter time than sodium hydroxide, 10 weight percent.

TEST 6 In this test, the effect of the sweetening process on the colorstability of the sweet naphtha was studied. The sour naphtha was athermal naphtha having a mercaptan number of 7 and a color of +14Saybolt. The sweetening was carried out at a temperature of 75 F. andthe aqueous solution contained a copper-ethylene diamine complex in anamount suflicient to have present 0.4 weight percent of copper. In Run11, the aqueous solution consisted of water, 13 sodium hydroxide, and12% of cresols. (No promoter polyamine was present.) The sour naphthawas sweetened in 6 minutes. The sweet naphtha was water-washed to removeaqueous solution and then was exposed to the atmosphere at 75 F. for 24hours. The color of the exposed naphtha was in the ASTM range, but waslighter than 1 ASTM. In run No. .12, the aqueous solution consisted ofparts of the solution of run No. 11 and 20 volumes of ethylene diamine.The sour naphtha was sweetened in 6 minutes. The color of the sweetnaphtha after exposure to the atmosphere at 75 F. for 24 hours was +8Saybolt. These runs show that the combination aqueous solution has avery pronounced favorable eifect on the color stability of the sweetnaphtha.

TEST 7 In this test, a flow unit was used in the sweetening of virginnaphtha having a mercaptan number of about 20 underconditions todetermine the loss of promoter polyamine to the sweet naphtha. In thistest, the catalyst was a copper-diethylene triamine complex and waspresent in an amount suflicient to introduce 0.15 weight percent ofcopper into the aqueous solution. The aqueous solution, excluding thepolyamine, consisted of water,

catalyst, petroleum cresols, 20 volume percent, and free The polyamineutilized in the tests was commercial grade diethylene triamine. Thetests were carried out at about 75 F.

The flow unit consisted of a reactor, sweetening zone, having a volumeof 350 ml. where the aqueous solution, sour naphtha, and air wereintermingled. The naphtha residence time in the sweetening zone was 14minutes. From the sweetening zone, the mixture passed to a disengagingzone where the aqueous solution separated from the naphtha. The naphtharesidence time in the disengaging zone was 10 minutes. From thedisengaging zone the oil and naphtha passed to a first settler whereinan aqueous phase was continuously separated by gravity settling fromnaphtha phase. The naphtha from the first settler was passed to a secondsettler for further removal of aqueous solution. The naphtha residencetime in each settler was 20 minutes.

In all the tests, the efiluent naphtha from the disengaging space wassweet; that is, the sweetening time under these conditions was less than24 minutes.

In the tests, an aqueous solution was used to contact 900 ml. of souroil. The sweet oil was then analyzed for polyamine content. Anotherportion of sour naphtha was then sweetened utilizing the separatedaqueous solution and the second portion of sweet naphtha was analyzedfor polyamine content. This procedure was repeated until the amine losshad become substantially constant.

Three aqueous solutions were utilized in this test. One solutioncontained 11 volume percent of diethylene triamine, another solutioncontained 7 volume percent of diethylene triamine, and the othersolution contained 4 volume percent of diethylene triamine. This amountof diethylene triamine was that present in the solution charged to thesweetening of the first portion of sour naphtha.

The results of this test are set out in the annexed figure which forms apart of this specification. The ordinate shows the grams of aminedissolved in each portion of the sweet naphtha produced. The abscissashows the number of portions of sour naphtha sweetened. Each portionamounts to 900 ml. of naphtha. The aqueous solution utilized in thesweetening amounted to 20 volume percent of the sour naphtha charged.

The figure shows that, quite surprisingly, a decrease from an initialconcentration of 11% of the polyamine to 7% results in substantiallyeliminating the loss of amine to the sweet naphtha. Utilizing 4 volumepercent of amine in the initial solution results in only a virtuallynegligible amount of loss of amine to the sweet naphtha.

Thus having described the invention, what is claimed 1. A sweeteningprocess which comprises contacting (a) a sour petroleum naphtha with (b)between about and 100 volume percent, based on said naphtha, of anaqueous solution consisting of (l) free-alkali metal hydroxide in aconcentration between about.5% and saturation, (2) alkyl phenolmercaptan solubility promoter in a concentration of between about 1volume percent and saturation, (3) water-soluble alkylene polyaminemercaptan solubility promoter in an amount between about 1 volumepercent and saturation, each alkylene group containing from 2 to 4carbon atoms, (4) a mercaptan oxidation catalyst consisting of thecopper-polyamine complex formed by the reaction of a water-solublecopper salt and an alkylene polyamine wherein the alkylene group isselected from the class consisting of ethylene and propylene, in anamount between about 0.02 and 1 weight percent, calculated as copper,and (5) the remainder essentially water, in the presence of suflicientfree-oxygen to convert essentially all the mercaptans in said naphtha,said contacting being carried out at a temperature between about 40 F.and 200 F. for a time sufiicient to convert essentially all of themercaptans in said naphtha, and separating an essentially sweet naphthafrom aqueous solution.

2. The process of claim 1 wherein said naphtha is a virgin naphtha.

3. The process of claim 1 wherein the polyamine promotor and thepolyamine in the complex is diethylene triamine.

4. The process of claim 1 wherein the alkyl phenol concentration isbetween about 10 and 20 volume percent.

5. The process of claim 1 wherein the promoter polyamine concentrationis between about 3 and 8 volume percent.

6. The process of claim 1 wherein the free-hydroxide concentration isbetween 10 and 15 weight percent 7. The process of claim 1 wherein saidtemperature is between about F. and F.

8. The process of claim 1 wherein the catalyst concentration is betweenabout 0.1 and 0.3 weight percent.

9. A sweetening process which comprises contacting a sour petroleumnaphtha with between about 5 and 100 volume percent, based on saidnaphtha, of an aqueous solution consisting of (1) free alkali-metalhydroxide in a concentration between about 10 and 15 weight percent, (2)alkylphenol mercaptan solubility promoter in a concentration betweenabout 10 and 20 volume percent, (3) alkylene polyamine mercaptansolubility promoter in an amount between about 3 and 8 volume percent,wherein each alkylene group contains from 2 to 4 carbon atoms, (4) amercaptan oxidation catalyst consisting of the com plex formed by thereaction of a water-soluble copper salt and an alkylene polyaminewherein the alkylene group is selected from the class consisting ofethylene and propylene, said catalyst being present in an amount betweenabout 0.1 and 0.3 weight percent calculated as copper and (5) theremainder essentially water, in the presence of sufficient free oxygento convert all the mercaptans in said naphtha, thereby producing a sweetnaphtha as determined by the Doctor test, said contacting being carriedout at a temperature between about 60 F. and 100 'F. for a timesufiicient to convert all of the mercaptans in said naphtha, andseparating a sweet naphtha from aqueous solution.

References Cited in the file of this patent UNITED STATES PATENTS2,413,945 Bolt Jan. 7, 1947 2,432,301 Fetterly Dec. 9, 1947 2,659,691Gislon et al. Nov. 17, 1953 2,663,674 Krause et al. Dec. 22, 19532,744,854 Urban May 8, 1956

1. A SWEETENING PROCESS WHICH COMPRISES CONTACTING (A) A SOUR PETROLEUMNAPHTHA WITN (B) BETWEEN ABOUT 5 AND 100 VOLUME PERCENT, BASED ON SAIDNAPHTHA, IF AN AQUEOUS SOLUTION CONSISTING OF (1) FREE-ALKALI METAL BYDIOXIDE IN A CONCENTRATION BETWEEN ABOUT 5% AND SATURATION, (2) ALKYLPHENOL MERCAPTAN SOLUBILITY PROMOTER IN A CONCENTRATION OF BETWEEN ABOUT1 VOLUME PERCENT AND SATURATION, (3) WATER-SOLUBLE ALKYLENE POLYAMINEMERCAPTAN SOLUBILITY PROMOTER IN AN AMOUNT BETWEEN ABOUT 1 VOLUMEPERCENT AND SATURATION, EACH ALKYLENE GROUP CONTAINING FROM 2 TO 4CARBON ATOMS, (4) A MERCAPTAN OXIDATION CATALYST CONSISTING OF THECOPPER-POLYALMINE COMPLEX FROMED BY THE REACTION OF A WATER-SOLUBLECOOPER SALT AND AN ALKYLENE POLYMINE WHEREIN THE ALKYLENE GROUP ISSELECTED FROM THE CLASS CONSISTING OF ETHYLENE AND PROPYLENEM IN ANAMOUNT BETWEEN ABOUT ABOUT 0.02 AND 1 WEIGHT PERCENT, CALCULATED ASCOPPER, AND (5) THE REMAINDER ESSENTIALLY WATER, UN THE PRESENCE OFSUFFICIENT FREE-OXYGEN TO CONVERT ESSENTIALLY ALL THE MERCAPTANS IN SAIDNAPHTHA, SAID CONTACTING BEING CARRIED OUT AT A TEMPERATURE BETWEENABOUT 40*F. AND 200*F. FOR A TIME SUFFICIENT TO CONVERT ESSENTIALLY OFTHE MERCAPTANS IN SAID NAPHTHA, AND SEPERATING AN ESSENTIALLY SWEETNAPHTHA FROM AQUEOUS SOLUTION.